1. Field of the Invention
The present invention relates to a laser shock peening apparatus, and more particularly, to a method and apparatus for utilizing a multiple beam dispenser in a plurality of laser peening cells.
2. Description of the Related Art
Laser shock peening is a process for improving the fatigue, hardness, and corrosion resistance properties of materials by focusing radiation on preselected surface areas of a workpiece. Laser shock peening the workpiece can avoid gross deformation, cracking, and spallation of the workpiece, and nonplanar workpieces can be laser shock processed without the need of elaborate and costly shock focusing schemes.
Laser peening, or also referred to as laser shock processing and laser shock peening, typically utilizes two overlays: a transparent overlay (usually water) and an opaque overlay, typically an oil based, acrylic based, or water based, black paint. During processing, a laser beam is directed to pass through the water overlay and is absorbed by the black paint, causing a rapid plasma formation and vaporization of the paint surface and the generation of a high amplitude shock wave. The shock wave cold works the surface of the workpiece and creates compressive residual stresses, which provide an increase in fatigue properties of the part. When using a water-based paint, a high-speed water jet quickly removes any remaining paint on the workpiece, and the workpiece surface is subsequently dried by the use of a high-pressure fluid or gas jet.
Finally, the workpiece is repositioned for further processing. A workpiece is processed by producing a matrix of overlapping spots that cover the fatigue critical zone of the part.
The entire laser-peening process occurs inside a peening cell, wherein a part manipulator positions the workpiece. Laser systems used for laser peening are typically interfaced to a single laser peening cell. Consequently, there are limits to the types of workpieces that can be laser peened with single-peening-cell configurations. Additionally, the laser system cannot be utilized during initial workpiece set-up and alignment, which results in significant loss of productivity and higher laser peening costs.
Having the foregoing in mind, it is a primary object of this invention to fully use the available laser time by dividing operational time into multiple peening cells. The utilization of multiple peening cells allows for two cells to be used at once, or for set-up and alignment or cell maintenance to be conducted in one cell while a second or alternative cell is used for peening and production. Furthermore, the invention allows for the construction of a variety of differently sized peening cells for treatment of various workpieces without necessitating additional laser systems.
The present invention is directed to a method and apparatus for utilizing multiple processing cells. The preferred embodiment of the invention comprises a multiple-beam laser for utilization in laser shock processing applications, and consists of multiple peening cells that better utilize the potential of the laser. In the invention, a plurality of peening cells share the operating time of a set of laser beams.
In one embodiment of the present invention, the peening cells vary in size, thereby providing for a small part manipulator in a first cell, and a larger part manipulator in a second cell. This embodiment would be useful in an application where target workpieces vary greatly in size, and the utilization of a smaller cell would be impossible, while the utilization of a larger cell for both large and small applications would be inefficient. A multiple-beam laser directed at a plurality of varying sized laser peening cells could be constructed to have, for example, two laser beams in a first cell, and two laser beams in a second cell. When additional beams are needed in one of the cells, mirrors could temporarily divert beams from another cell.
In another embodiment of the present invention, a multiple laser beam system could be directed into a first peening cell, and redirected to a second peening cell upon an operator""s command, either by physically moving the entire laser, or by utilizing a system of mirrors.
Yet another embodiment of the present invention further comprises a logic control device for controlling the usage of the varying peening cells, thereby optimizing the efficiency of the laser system.
The invention can also be expressed in the form of a method, wherein a first pulse of energy is created, the first pulse of energy is directed into a first peening cell, a second pulse of energy is created, the second pulse of energy is directed into a second peening cell, and the process repeats itself as determined by a job-sensing microprocessor.
An advantage of the present invention is that each pulse of the laser energy can be utilized. In the present laser peening systems, many laser pulses cannot be utilized because the workpiece is not available to be processed.
The system, in another embodiment of the invention, allows for utilization of each potential laser pulse, i.e., flashlamp pump pulse (or diode pumping pulse for diode pumped systems) through time sharing.
Another advantage of the present invention is that more workpieces can be produced in a given amount of operation time.
Yet another advantage of the present invention is that with use of multiple peening cells, it is possible that while one cell is down for repair or for setting up a new workpiece, the laser can continue to process other parts in the other peening cells. This way the laser is in continuous use, maximizing its use and minimizing wasted flashlamp pulses.